<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>em</title>
    <style type="text/css">
        body{font-size: 70%;}
        .p1{font-size:2em;}
        .p2{font-size:1.6em;}
    </style>
</head>
<body>
<p class="p1">em现对于当前文档内文本的字体尺寸</p>
<p class="p2">em现对于当前文档内文本的字体尺寸</p>
</body>
</html>